The existence of neoplastic cells emphasizes two important biological questions. First, what are the functional elements that regulate the patterned growth of tissue? Second, how do changes in these regulatory functions result in the development of neoplastic cells? We have been analyzing two temperature-sensitive neoplastic mutants of Drosophila, 1(2)g1ts and Tum1, to determine the effect of these mutations on the ability of cells to maintain their determined state, to perform differentiated cell functions, and to participate in the processes that regulate cell growth. The analysis of the 1(2)g1ts allele demonstrates that the 1(2)g1+ function is required both during the development of the mature wing disc and to maintain the organized structure of the mature wing disc. Since this neoplastic transformation is apparently irreversible, experiments will be performed to determine the time required to initiate neoplastic development and to determine the cytological and ultrastructural consequences of the initiation of the wing disc neoplasm. Experiments will also be performed to determine the ability of specific regions of the 1(2)g1ts wing disc to undergo neoplastic development and the ability of these regional neoplasms to stimulate the regeneration of wild-type tissue. Using genetic markers, the developmental fate of neoplastic lymph glands from Tum1 larvae will be analyzed to determine the cell types produced during culture in adult hosts and the cytological and ultrastructural consequences of the neoplastic transformation. In addition the effect of Drosophila parasites on the development of the neoplastic lymph gland will be analyzed.